1. Field of the Invention
The present disclosure relates to a gas insulated switchgear, and particularly, to a switchgear devised to open or close an electric power transmission line and extinguish an arc generated in performing an insulating or breaking operation by using a gas.
2. Background of the Invention
In general, a switchgear refers to a device that opens or closes an electric load or breaks a current when an accident or a fault such as ground fault, short-circuit, or the like, in a transmission and substation (or transformation) system or in an electrical circuit. In particular a gas insulated switchgear includes a breaking part disposed in a tank-type enclosure charged with SF6 insulating gas as a tasteless, odorless, nontoxic inert insulating gas having excellent insulating properties. In the gas insulated switchgear, an electrical line in use may be opened or closed manually or may be opened or closed by an actuator, or the like, installed outside of the enclosure remotely. In the event of an overload or short-circuit, the gas insulated switchgear automatically breaks a current to protect an electric power system and electric load devices.
As mentioned above, the gas insulated switchgear includes a stationary contact arm and a movable contact arm installed in a breaking part thereof. Normally, the stationary contact arm is in contact with the movable contact arm to allow a current to flow, and in a case in which a large current flows due to fault current on an electric power line, the movable contact arm and the stationary contact arm are separated quickly to break such a large current.
Here, the actuator moves a cylinder rod connected to a cylinder by actuating power generated from a spring, or the like, charged by hydraulic pressure, pneumatic pressure or a motor to a breaking position, and when insulating arc-extinguishing gas is compressed within a compression chamber according to the movement of the cylinder rod, the compressed arc-extinguishing gas having high pressure is jetted to an arc to cool and extinguish the arc to accomplish breaking the circuit. Thus, the breaking operation to break a fault current requires a high degree of actuating power, relative to a connection (in other words “closing”) operation. In addition, in order to enhance breaking performance, the movable contact arm needs to be separated from the stationary contact arm as quickly as possible, and even after the separation of the movable contact arm, preferably, a distance between the movable contact arm and the stationary contact arm is maintained as large as possible.
Namely, at an initial stage of a breaking operation, the movable contact arm should overcome frictional force between the stationary contact arm and the movable contact arm and pressure of the arc-extinguishing gas to move, so resistance with respect to movement of the movable contact arm is increased, relative to a closing operation. In addition, in order to reduce a time during which a fault current flows as much as possible, the movable contact arm should be separated from the stationary contact arm at a very fast speed.
To this end, however, a large capacity actuator is required. In detail, in order to increase actuating power, a large capacity spring needs to be used, which, however, results in an increase in a volume of the actuator. In addition, in order to stably support the large capacity spring, strength of a structure fixedly supporting the spring needs to be increased, further increasing the volume of the actuator.
Thus, there is a need to quickly perform a breaking operation without greatly increasing the volume of the actuator, and U.S. Pat. No. 7,528,336 discloses an example. In the related art, high torque is allowed to be transmitted at an initial stage of a breaking operation by adjusting a configuration and a disposition angle of a link member connecting a lever of a actuator and a rod of a movable contact arm to thus quickly perform a breaking operation. In detail, in the related art, a breaking operation is quickly performed by applying maximum torque to the link member by actuating power at an initial stage of the breaking operation. In particular, in the related art, operational characteristics at the initial stage of the breaking operation are improved by making the use of the fact that a prompt operation is not necessary in case of a circuit closing operation, relative to the breaking operation.
However, even with the related art, a time during which maximum torque is transmitted is too short and the decrement of torque based on a movement of a movable contact arm is too large, so it is difficult to obtain a sufficient breaking speed. Namely, in order to perform a breaking operation with maximum acceleration force at the initiation of the breaking operation, maximum torque needs to last as long as possible or the decrement of torque needs to be small, but in the related art, it is impossible to adjust the duration or the decrement.
In addition, in order to maximize acceleration with which the movable contact arm is moved in a state in which the breaking operation is performed to a degree, the better a time interval during which maximum torque and minimum torque is applied is shorter, but with the related art, it is impossible to adjust the time interval.